The present invention relates to a zoom lens for image capturing elements which has a long back focus that allows a color separation prism to be inserted, and is compact despite a high variable magnification, to be used favorably in a video camera.
In recent years, with digitization of a video recorder or the like, a video camera is also required to have high image quality. As an effective means for high image quality, there is given a multiple-plate type wherein a ray of light after photographing is separated by a color separation prism into respective colors of R (red), G (green) and B (blue), and three CCDs (Charge Coupled Device) each corresponding independently to each color are used for image-capturing, whereby images are superposed to obtain high image quality. In the video camera of this kind of a multiple-plate type, there is a strong demand for the zoom lens which has a long back focus that allows a color separation prism to be inserted, and has a high variable magnification.
Namely, in the video camera of a multiple-plate type of this kind, a relatively long back focus is needed and a long exit pupil distance which does not cause color shading is necessary, for arranging a color separation prism, compared with a single-plate type representing a combination of a single CCD and a color filter.
Incidentally, Patent Document 1, for example, discloses a zoom lens which has a long back focus and has a ratio of variable magnification of about 10.
(Patent Document 1) TOKUKAIHEI No. 07-270684
(Disclosure of The Invention)
(Problems to be Solved by the Invention)
However, the zoom lens disclosed by Patent Document 1 has a problem that the number of constituent lenses is as relatively large as 13–14, causing cost increase and weight increase, although its long back focus allowing a color separation prism to be inserted is realized.